Voltage Controlled Oscillator (Vco) - Nokia NPL-4 Series Troubleshooting Instructions

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• Reference frequency for the PLL synthesizer.
• System clock for BB (signal VCTCXO = 26 MHz, output REFOUT of the
Helgo ASIC N500).
For an error free initial synchronization, the 26MHz frequency of the reference oscillator
must be accurate enough. Therefore, an analog voltage with signal name AFC tunes the
oscillator.
The AFC voltage is calculated using the values "AFC value" and "AFC slope", which are
determined during Rx calibration of the low band.

Voltage Controlled Oscillator (VCO)

The VCO is able to generate frequencies in the range of 3296MHz to 3980MHz when the
PLL is working properly. The frequency of the VCO signal is divided by 2 or by 4 in the RF-
ASIC. This allows the generation of all the frequencies in the GSM850, GSM900,
GSM1800 and GSM1900 bands, both RX and TX range.
The output frequency of the VCO is controlled by a DC voltage (Vc) of the PLL loop filter.
The valid range of Vc is 0.7V– 3.8V when the PLL is in steady state. The typical tuning
sensitivity is 250MHz/V.
Even if the PLL is not working properly (Vc outside the valid range), a frequency at the
output of the VCO can be detected between 3GHz and 4.4 GHz (if the VCO itself is ok and
the supply voltage VR7 = 2.78V is available).
Copyright © 2005 Nokia Corporation. All rights reserved.
Issue 2 05/05
Company confidential NPL-4/5/
Troubleshooting Instructions
Page 49